Hearthstone's new expansion is slated for release next month, and it marks the return of one of the most legendary original characters to come out of Blizzard's collectible card game. The Boomsday Project launches on August 7, and it places the wild Dr. Boom in a starring role. It will feature 135 new cards, new card types and keywords, and a distinct focus on Mechs.

The biggest new addition comes in the form of Legendary spells, which promise much bigger impacts than ordinary spells. Hearthstone began with only Legendary minions but has expanded the Legendary feature to Quests, Heroes, and Weapons, so Spells are the last remaining card type. The announcement teased that each spell is the product of some mad scientist recruited by Dr. Boom, so those are likely to make appearances as class Legendary minions that synergize with their signature spells.

A new keyword is being introduced as well. Mechs will come with the "Magnetic" keyword, letting you merge them together to combine their attack, health, and abilities. This appears similar to the Hunter "Deathstalker" hero power with Beasts.

Finally, two new card types are being introduced without special keywords. "Projects" are spells that benefit both players, meant to challenge you to build your deck strategically so you can take better advantage of the benefits. Omega cards get a big bonus if you play it once you have 10 Mana crystals, encouraging you to save some otherwise early minions for the late game.

Click image to view new cards.

A single-player component will follow two weeks after the launch of the expansion. On August 21, The Puzzle Lab will open. Unlike the boss challenge or dungeon-crawling single-player portions from previous expansions, this round will focus on different puzzle types: Lethal puzzles, which challenge you to find the winning play, and Survival puzzles, which require you to stay alive against overwhelming odds.

Logging in during the launch event will net you a free random class Legendary and three Boomsday Project card packs. You can also purchase a 50-pack bundle for $50 that includes a free golden class Legendary and a Mecha-Jaraxxus card back. A separate 80-pack bundle for $80 will also include the Mecha-Jaraxxus Warlock Hero (above). The announcement notes that each can only be purchased once per account, which would seem to indicate that you could buy both if you want 130 packs for a better price than average.